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Vensim Help

You can use the keyword :NA: where a variable name or number would normally appear. :NA: takes on a special value (-2109 ) that can be used to test for the existence of data.  "Data Equations" below gives an example of how to test for the existence of data at a given time using :NA:.

If you assign a variable the value :NA: at any time the value will not appear in graphs (it will be ignored or interpolated over) and will show up as only "—" in tables.